Bloody hell... 14 is EFAULT. And that - from sys_mount() called bytask that has KERNEL_DS as addr_limit. What options do you pass to kerneland what filesystems are compiled in? Actually, adding printk("%s\n", p);in the same place might give some hints...

Basically, sys_mount() is called in conditions when -EFAULT should notbe generated at all - it is handled on a pretty low level and AFAICSthat area hadn't been changed between -pre2 and -pre3. Weird...